1. Field of the Invention
The invention relates to a method and apparatus for the scanning of an object by means of ultrasound using an ultrasonic transducer array comprising a number of transducer elements lying side by side wherein for at least some of the transducer elements the output signals delivered upon reception of echo signals can be time-delayed. Preferentially, it involves an ultrasonic scanning method for a linear, trapezoidal or phased-array system which is used in the medical sector for the examination or patients and which serves for the imaging of structures inside the body.
2. Description of the Prior Art
In ultrasound diagnostic equipment and, in particular, transducer array devices, the imaging quality is substantially improved by focusing. In a pivoting system, that is, e.g., in a so-called phased-array system, in addition to focusing, long delay times which are required for adjustment of the control angle must be made available. To obtain high resolution, and for simultaneous extensive restriction or even prevention of grating lobes, the receiving delay unit of the array system must have a plurality of parallel channels, e.g., 64 in a phased-array system. Such channels are quite expensive because of the required high accuracy of adjustment.
Therefore, to provide an inexpensive ultrasonic scanner, the number of active delay channels should be reduced.
In a conventional phased-array or linear-array system, focusing on a fixed point is carried out by adding up the output signals of all transducer elements of the reception aperture (e.g. N=64) simultaneously. The advantage of this method is that one can operate at maximum frame frequency. This is of great importance, especially in cardiological applications, where high speed signal processsing is essential. In applications in the abdominal region, the parameter "resolution" is of greater importance. Here, a certain loss (tradeoff) of frame frequency in favor of resolution is acceptable, because as a rule only slowly changing processes are being imaged.